Approximately 5% of patients with psoriasis go on to develop inflammatory polyarthritis, for which there is no know cure. Standard treatment regimens involve the use of immunosuppressive medications. This study is designed to determine an optimal biological dose of the immunosuppressive antibody, hOKT3y1 (ALA-ALA). Additionally, it will provide a preliminary evaluation of the immunosuppressive properties of the antibody when this optimal dose is achieved.